"Five out of the eight tuna species are at risk of extinction, conservationists warned today, as they called for urgent action to tackle over-fishing.

The latest assessment for the International Union for Conservation of Nature (IUCN) showed that three species are threatened with global extinction, while two more will be under threat without action to help them.

A study, published in the journal Science, which looks at all "scombrid" fish, which include tuna and mackerel, and billfishes, which include swordfish and marlins, found that seven of the 61 known species were under threat.

The study said some of the species were heavily over-fished, with little interest in conserving them because of the high commercial value of the catch."